Cumulative lead exposure and cognitive performance among the elderly in Johannesburg, South Africa

Q2 Environmental Science

Environmental Advances Pub Date : 2025-06-21 DOI:10.1016/j.envadv.2025.100652

Tahira Kootbodien , Nisha Naicker , Renee Street , Angela Mathee

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Abstract

Background

Lead (Pb) is a known neurotoxin, but evidence linking low chronic exposure to cognitive performance, particularly in low- and middle-income countries, remains limited.

Objectives

This study examined cumulative bone lead exposure and cognitive performance in older adults living in care facilities located near mines and mine tailings in Gauteng Province, South Africa.

Methods

We included 139 participants aged 60 to 80 years from state-owned elderly assisted living facilities in City of Johannesburg Municipality, Gauteng. Cumulative lead exposure was measured in the tibia using K-X-ray fluorescence (KXRF). Cognitive performance was assessed using the Early Dementia Questionnaire (EDQ) and the Cambridge Neuropsychological Test Automated Battery (CANTAB), focusing on memory, executive function, attention and psychomotor speed. We examined associations between cumulative bone lead levels and cognitive outcomes using multiple regression models, including quadratic terms to test for nonlinearity. Models were adjusted for age, sex, education, and smoking status.

Results

Participants had a mean age of 69.9 years (54 % male); 30 % reported occupational lead exposure or had been engaged in lead-related activities. Mean bone lead levels were 8.1 µg/g (SD 6.4), and 55 % of participants met criteria for mild cognitive impairment (EDQ ≥ 8). Higher cumulative bone lead levels were associated with poorer cognitive performance: each unit increase in bone lead was associated with a 10 % higher rate in reaction time (RTI) (adjusted IRR = 1.10; 95 % CI: 1.03–1.16). A significant bone lead-sex interaction was observed (p = 0.03), with a stronger association in women (IRR = 1.11, 95 % CI: 1.03–1.19) than in men (IRR = 1.05, 95 % CI: 1.00–1.10), suggesting potential sex-specific effects. A nonlinear association was observed between bone lead and spatial working memory (SWM) errors (β = 0.022, 95 % CI 0.013-0.032), with task errors increasing disproportionately at higher lead levels, indicating worse cognitive performance of memory-related tasks with increasing exposure.

Conclusion

This exploratory study suggests low-level cumulative Pb exposure may be associated with poorer cognitive function in the elderly, particularly affecting executive function and impulse control. Larger studies are needed to confirm these associations.

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南非约翰内斯堡老年人的累积铅暴露与认知能力

铅（Pb）是一种已知的神经毒素，但是，特别是在低收入和中等收入国家，将低水平的慢性接触与认知能力联系起来的证据仍然有限。目的：本研究调查了居住在南非豪登省矿山和尾矿附近护理机构的老年人的累积骨铅暴露和认知能力。方法纳入来自豪登省约翰内斯堡市国有老年辅助生活机构的60 ~ 80岁的139名参与者。利用k - x射线荧光（KXRF）测量胫骨累积铅暴露。采用早期痴呆问卷（EDQ）和剑桥神经心理测试自动化电池（CANTAB）评估认知表现，重点关注记忆、执行功能、注意力和精神运动速度。我们使用多元回归模型检验了累积骨铅水平与认知结果之间的关系，包括二次项来检验非线性。模型根据年龄、性别、教育程度和吸烟状况进行了调整。结果参与者平均年龄为69.9岁（男性占54%）；30%的人报告职业性铅接触或曾从事与铅有关的活动。平均骨铅水平为8.1 μ g/g (SD 6.4)， 55%的参与者符合轻度认知障碍标准（EDQ≥8）。较高的累积骨铅水平与较差的认知表现相关：骨铅每增加一个单位，反应时间（RTI）率就会增加10%(调整IRR = 1.10；95% ci: 1.03-1.16)。观察到显著的骨铅-性别相互作用（p = 0.03），与男性（IRR = 1.05, 95% CI: 1.00-1.10）相比，女性（IRR = 1.11, 95% CI: 1.03-1.19）的相关性更强，提示潜在的性别特异性影响。研究发现，骨铅与空间工作记忆（SWM）错误之间存在非线性关系（β = 0.022, 95% CI 0.013-0.032），任务错误在高铅水平下不成比例地增加，表明记忆相关任务的认知表现随着接触量的增加而变差。结论本探索性研究提示低水平累积铅暴露可能与老年人认知功能下降有关，特别是对执行功能和冲动控制的影响。需要更大规模的研究来证实这些关联。

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